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Oxidation
Process in which atoms or ions attain a
more + oxidation state
Ex.
Na → Na+ + e
Cl- → Cl + e
Ca+ → Ca2+ + e
Reduction
Atoms or ions of elements attain a more
negative oxidation state
Ex.
Cl + e → ClMnemonic: “OIL RIG”
Oxidation involves loss, reduction
involves gain
Oxidation Number
Uncombined elements have oxidation # of 0
Monoatomic ions have oxidation # equal to
their ion charge
F is always –1 in a compound
O is almost always –2 in a compound
H is +1 in all compounds except those with
metals (then its –1)
More electronegative element is assigned a
number equal to its ion charge
Algebraic sum of oxidation numbers in a
compound is always zero
Practice
Determine the oxidation numbers for each
element in the compounds below
NaCl
H2SO4
AgNO3
CO2
SF6
NO3-
Redox Reactions
Redox reactions are among the most
common of all chemical processes
Combustion, synthesis, decomposition,
and single replacements are all redox
reactions
Definition
Reaction in which a change in oxidation
number occurs
Oxidation – becomes more positive
Reduced – becomes more negative
Oxidation and reduction always come in
pairs
Oxidizing Agent – substance reduced
Reducing Agent – substance oxidized
Example
In the reactions below, identify what is
oxidized, what is reduced, the oxidizing
agent and the reducing agent
2PH3 + 4O2  P2O5 + 3H2O
2H2O + Al + MnO4-  Al(OH)4- + MnO2
More Examples
For each, write the reaction, then
identify what is oxidized, what is
reduced, the oxidizing agent and the
reducing agent
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